The invention in general relates to nuclear magnetic resonance (NMR) spectroscopy, and in particular to sample tube assemblies for NMR.
Nuclear magnetic resonance (NMR) spectrometers typically include a superconducting magnet for generating a static magnetic field B0, and an NMR probe positioned within a bore of the magnet. The NMR probe includes one or more special-purpose radio-frequency (RF) coils for applying a time-varying magnetic field B1 perpendicular to the field B0 to samples of interest, and for detecting the response of the samples to the applied magnetic fields. The samples of interest are normally held in sample tubes or in flow cells.
Spinning NMR sample tubes at high speeds (e.g. at a frequency of several kHz) during measurements can lead to narrower spectral linewidths. Spinning the samples causes the NMR measurements to reflect an azimuthal averaging of gradients and inhomegeneities in the magnetic fields applied to the samples. For solid polycrystalline samples, spinning also allows azimuthally averaging over the various crystalline orientations present in the sample. For solid samples, optimal spectra can be achieved when the angle between the spinning axis (the longitudinal sample axis) and the direction of the static magnetic field is the xe2x80x9cmagic angle,xe2x80x9d or about 54xc2x0. The magic angle is the solution to the equation 3 cos2xcex8xe2x88x921=0. Liquid or gaseous samples are typically spun about an axis coinciding with the direction of the static magnetic field.
In a commonly-used approach, a rotor (spinner) turbine having a frusto-conical bottom surface is disposed above a matching frusto-conical stator (fixed housing). A sample tube is inserted through a central hole in the rotor, and is secured to the rotor. Running air upward along the sample tube surface causes the rotor to levitate and spin about its longitudinal axis. For further information on prior art spinning methods and/or sample tube assembly designs see for example U.S. Pat. Nos. 4,739,720, 4,275,350, 4,088,944, 3,681,683, and 2,960,649.
The present invention provides a nuclear magnetic resonance sample tube assembly for holding a nuclear magnetic resonance sample, comprising: a sample tube defining a sample holding chamber for holding the sample; a scaling plug for sealing a sample within the sample tube, comprising a generally-longitudinal filling part for filling a part of the sample tube, and a sealing part protruding transversely relative to the filling part; and a clamp for clamping the sealing part to the sample tube using a longitudinal force.
In a preferred embodiment, the clamp is a rotor for spinning the sample tube assembly. Preferably, the sample tube has a sealing flange protruding from an exterior of the sample tube along an inlet region of the sample tube. The filling part is sized to maintain an air escape clearance between the filling part and the sample tube for allowing air to escape out of the sample tube as the filling part is inserted into the sample tube. The sealing part contacts the sealing flange to seal the sample holding chamber. The rotor abuts a side of the sealing flange opposite the sealing part and secured to the sealing part, for clamping the sealing part to the sealing flange. The rotor can have a plurality of rotor blades for spinning the sample tube assembly in response to a gas flow along the same tube.